Chang writes: AT&T is planning to move residential users to carrier grade NAT as part of their IPv6 rollout.

AT&T says it is not going to adopt dual-stack mode – where native IPv6 and IPv4 services run side-by side – for its residential customers
"We're going into address conservation mode, which is the guidance of [the American Registry for Internet Numbers],'' Fitzsimmons says. "We're stemming the consumption of IPv4 addresses for both our enterprise customers and any customers paying for static IP addresses. For the gross majority of our customers, as they go through IPv6 testing and trials, the majority of our customers will take advantage of carrier-grade NAT."